Computer networks typically provide a physical interconnection between different computers to allow convenient exchange of programs and data. A plurality of connectivity devices, such as switches and routers, interconnect each user computer connected to the network. The connectivity devices maintain routing information about the computers and perform routing decisions concerning message traffic passed between the computers via the connectivity devices. Each connectivity device, or router, corresponds to a network routing prefix indicative of the other computers, which it has direct, or indirect access to. Therefore, data routed from one computer to another follows a path through the network defined by the routers between the two computers.
The routers define nodes in a network, and data travels between the nodes in a series of so-called “hops” over the network. Since each router is typically connected to multiple other routers, there may be multiple potential paths between given computers. Typically, the routing information is employed in a routing table in each router, which is used to determine a path to a destination computer or network. The router makes a routing decision, using the routing table, to identify the next “hop,” or next router, to send the data to in order for it to ultimately reach the destination computer. However, network problems may arise which render routers and transmission paths between routers inoperable.
There are two families of path characteristics, and the verification/diagnostics there of, that are of particular interest when considering network-based Internet Protocol (IP) Virtual Private Networks (VPNs). The first family of path characteristics relate to path verification in terms of basic connectivity. The second group of characteristics of interest to a customer of a network-based VPN fall under the umbrella of real-time statistics. These real-time statistics can be defined as the ability for a customer edge (CE) router to obtain real-time statistics related to a particular path used by that CE to carry its traffic across the core of the network-based VPN provider. Such attribute properties include (but are not limited to) delay (one way and round trip), jitter, and error rate (i.e. packet loss/error). Currently these types of statistics are provided by some service providers, but are based largely on average values that are insufficient for the customer to compute real-time path characterization.
Up-to-the-minute values for various path characteristics such as delay and jitter are desired in order to qualify a particular path on a real-time basis so as to ease troubleshooting should some path characteristics such as the delay be detected as abnormally high, make instantaneous repairs to broken paths, or in order to choose alternate paths (i.e.: change routing behavior so as to obscure the network defect from the customer), or just to obtain information as to whether the requested path attributes are being delivered by the core network at any given point in time.
Certain applications, such as the Service Assurance Agent (SAA) available from Cisco Systems, Inc. of San Jose, Calif., may be used by the customer between their customer edge routers to verify the end-to-end path using IP protocol packets. These provide important information about the overall end-to-end path, but do not provide any direct information about the critical core network paths between the provider's PE routers that actually carry the IP traffic between their sites. For this reason the customer is unable to ascertain in which segment of the network a particular problem is located, or what specific path characteristics are being delivered at any particular point in time. Such information could be used by a network-based IP customer to trigger appropriate QoS parameter setting adjustment on their PE to CE links, trigger a local link update and so on, should an Service Level Agreement (SLA) degradation cause be located on such links. This information must be gathered by the Service Provider using MPLS-specific tools and algorithms to assure their accuracy and their efficiency when used to correct any defects detected by them.
In a particular example, a client has the ability to identify a set of “important” destinations for which the gathering of the path attributes is required on a real-time basis (because of the necessity to measure the performance of a particular path). Note that the term “real-time” does not refer to the frequency at which path attributes are retrieved but is used to illustrate the fact that such information is gathered upon an explicit request of an authorized CE. The client is able to identify the set of important destinations which to gather path attributes.
Many label switched paths may be used to transport the traffic for many different applications such as Traffic Engineering or MPLS L3 VPN between end points of the MPLS network. In some cases, these paths may contain many parallel equal cost branches called load-share paths (LSPs). These paths may be rather divergent as they traverse the network, but ultimately terminate at the same end points. These paths allow traffic to be better distributed across equal cost links, thereby better utilizing the available bandwidth in the network. Load-share paths, although an advantage in its own right, also pose a potential difficulty in the way of testing each one of these paths for characteristics. Further adding to this difficulty is the fact that only a subset of these LSPs are in use by any given VPN at any given point in time. The actual choice of paths is also largely dependent on the local forwarding decisions made by specific types of forwarding hardware (i.e.: routers).